Printing control circuits for photoelectric engraving machines



M. FARBER Feb. 25, 1958 PRINTING CONTROL CIRCUITS FOR PHOTOELECTRICENGRAVING MACHINES 2 Sheets-Sheet 2 Filed Dec. 8, 1953 MONROE FARM/Q;

INVENTOR. WQW

// Tr'y entitled United States Patent 'Otiice PRINTING CONTROL CIRCUITSFOR PHOTO- ELECTRIC EN GRAVIN G MACHINES Monroe Father, Jericho,

Camera-and Instrument Delaware Application'December 8, 1953, Serial No.396,952

' SIClaims. (Cl. 1786.6)

N. Y., assignor to Fairchild Corporation, a corporation of .machine ofthe type disclosed in U. S. patent to'Boyajean,

INo.-2,575,546, issued November 20, 1951, to the assignee of the presentapplication. In some respects, the appa- Iratus' to' be describedhereinis also related to that dis- .closed in thecopending application ofMonroe Farber,

Characteristic Correction System for Photo- :electric EngravingMachines, filed December 8, 1953, LSerp No. 396,953, and also assignedto the'owner'of'ithe present application. Such part ofthe abovementioned iprior"disclosures-as'is'essential for an understanding of:the instant invention 'is' shown and described herein, but additionaldetails not related directly to the present invention-maybe obtained byreferring to. those .prior cases.

In general, machines of the type-with whichthisapplication is concerned"are intended for the :making. of printing plates bythephotoelectrically' controlled'engraving of a-suitableplate-material,usually aplastic sheet, by

burning oncutting ind'entationstherein inresponseto anelectricsignal-obtained by scanning an original such as a photo'graph.The' pattern in which the indentations or individual excavations are 1produced 'upon the engraving .plate is controlled by 'mixing-the signalof the scanning device with a tone frequency whose frequency andamplitude :are relatively fixed. If the degree of penetra- -tion of'thestylus'into the sheet 'material is related to'the magnitude of' 'thescansignal, and if t the stylusis of proper shape, the dot structure 'of thefinal engraving .plate will have a uniform screen pattern defined'by'regularlyspaced' excavations or recesses whose size depends upon:the point-to-point reflectivity of corresponding por- .tions oftheoriginal subject matter.

a Machines-.ofxthis type have been provided with various kinds.ofzcontrol: circuits and: adjustments whose purpose .is to permit theoperator to produce asatisfactory en- :graving under:Idiiferentconditions, and particularly from original tmatter having differentreflection or tone scale characteristics. .Thus;.the'patent referredto-above pro- ..vides a so-called whitelevelzcontrol which in effectvaries .ihermagnitude of the --amplified output of a photoelectricauxiliary or additional control circuits, and adjustable 1 elements,for-machines of this type, whereby the operator 2,824,995 :FatenteclFeb. 25, 1958 from which stereotype plates can be duplicated in a wellknown manner, and since the suitability of an engraving so prepared willultimately be-judged in terms of a printed copy produced thereby, it isapparent that other factors besides the nature of the original copy orphotograph should-be considered. A principal factor of this type isconcerned with the particular nature of the printing process to be used,such as the kind of press, the kind of paper to be printed, the inkused, and so forth. With prior machines, while (given enough time) avery skilled operator might be able to make allowance forthese factorsin the'preparation of the plate, the results are far from uniform andcannot be obtained with any accuracy by the ordinary user ofthe'equipment. It is accordingly a principal object of thepresentinvention to provide can make the desired correction in theengraving process to compensate-for factors introduced in the use of theengraver plateafter it has been prepared.

A further object of the invention is to provide a printing controlcircuit for inclusion in machines of the above type,-which will involveonly comparatively simple additions and-modifications in more usualcircuits which do not include this feature.

Still another object of the invention is .to provide a circuitforphotoelectric engraving machines which will include, in-addition toblack and white level, controls, a

control for establishing a predetermined and desired minimum hole sizein the final engraved plate, in accordancewith foreknowledge ofthe'printing process in which the plate is to be used. As here employed,the term hole size refers to the area of the indentation or cavityproduced in the engraving plate by the stylus, it being understood thatunder ordinary conditions this hole does not actually pass completelythrough the material of the plate. The establishment of a minimum holesize, where scanningrmeansbefore applying it to further. amplifiers theproduct is a planographic printing plate, establishes a-maximum ratio ofprinting area tonon-printing area in'the blackest portions of the plate.

Theabove and other objects of the invention will best 'be understoodbyreferring now to, the following detailed specification of apreferred'embodimentthereof, taken in'connection with the appendeddrawings, in which:

'Fig. 1 is'a schematic view illustrating the principal parts ofaphotoelectric engraving.machinetogether with a combined block andschematic diagram of the electrical channels involved in the invention,

1 'Fig. 2 is a graphical presentation relating stylus motor amplitude tovarious values of smallest hole size,

'Fig. 3 is a typical wiring diagram for an addition vcircuitwhich may beused in the invention, and,

Fig. 4 is a similar diagram of a typical subtraction circuit.

As shown in Fig. 1 of the drawings, the general arrangement of theapparatus, in so far as concerns the scanningand engraving devices,.andthe drive system and screen tone generator, may be, identical with thoseshown in the prior patent and the copending application referred toabove. By way of review, it may be pointed out that the machinecomprises the cylinders 10 and 12, mounted for synchronous rotation upona common shaft 14'which may be'driven as by reduction gearing 16 from amotor'18. 'One of the cylinders, such as cylinder 10, isarranged to havesecured therearound an original, such as aiphotograph, of which anengraving is to be made. A carriageZt) is mounted to reciprocate along:a path parallel to the axis of cylinder 10, as upon guides (not shown),.and carries a suitable light source 22 directed. upon .a-, smallspot ofthe original, from which the light is reflected to a photocell 24 alsoon carriage 29, so that the photocell output is a function of therefiec- 3 tivity (or reflection density) of the successive regions ofthe original scanned by the device.

Cylinder 12 also has a carriage associated therewith, the same beingdesignated 26, guided like cylinder and carrying the magnetoelectricstylus motor and stylus indicated generally by 28. Cylinder 12 carrieswrapped around it a plastic or like engraving sheet upon which thestylus cuts, burns, or otherwise forms an engraved image correspondingto the matter shown on the original copy sheet of cylinder 10. As morefully described in the prior patent referred to above, the carriages arecon nected to reciprocate alongside their respective cylinders inopposite directions as by being connected to opposite runs or passes ofan endless flexible and inextensible belt-like connector 30 carriedabout opposite pulleys 32 and 34. One pulley is driven bysuitablegearing, denoted by 36, from the same motor or gearing whichrotates the cylinder shaft 14. Thus, the photocell system and the stylussystem are reciprocated in timed relation to the cylinder rotation, andthe illuminated spot and stylus trace out scanning helices upon thelayers carried by their respective cylinders.

Since the final engraved plate must carry a representation equivalent toan ordinary screened printing plate for half-tone work, the apparatusincludes means for generating a pattern signal governing the engravingmotion of the stylus in a regular fashion, such signal beingincorporated into the photocell output, as amplified and applied to thestylus motor. Such a generator is shown at 38 as driven synchronouslyfrom shaft 14, the details thereof being given in detail in the priorpatent. The tone output, suitably amplified by a conventional amplifier40, is applied to energize the gaseous illuminating lamp 22 over thepath 42, and thus to modulate the photocell output voltage which alsorepresents the variations in reflectivity of the original copy oncylinder 10, and the tone signal is also applied through other ampli=fiers and controls to the stylus motor 28.

The signal applied to the stylus motor is thus a composite signal madeup of a component of fixed frequency and constant but adjustableamplitude, from the tone generator and intervening amplifiers andcontrols, and a component from the photocell and its output circuitwhich may be thought of as a varying direct current derived from thevariations in reflection density of the original copy, superimposed ormodulated upon a carrier at tone generator frequency injected by reasonof the energization of the exciting lamp 22 from the generator 38. Inthe patent mentioned above, these two components are referred to as theblack level signal and the white level signal, respectively, so calledbecause in making a normal engraved plate, adjustment of the black levelsignal will control the minimum penetration of the engraving stylus(that is, in the absence of any illumination from the copy to thephotocell), while the white level signal will control the magnitude oftheincrease in pene tration resulting from the scanning of an area ofthe original which is capable of reflecting any sensible amount of lightinto the cell.

The manner of adjusting this apparatus for making suitable engravingsfrom a particular original subject, such as a photograph, is describedin detail in the prior cases, and since this procedure is not essentialto the present invention, such description is omitted.

In the copending application, there are described the connections fromamplifier 40 to ganged potentiometers 44 and 46 from the adjustabletake-offs or contacts of which potentials are derived to control thestylus motor 28. As there described, the output of potentiometer 44 issubtracted from the amplified outputof the photocell 24, as by asubtraction circuit, and the difference signal passes through a tonecompensator to an addition circuit where it is added to the output frompotentiometer 46 and the modified voltage so obtained is amplified andapplied to the stylus motor 28.

In the present improvement, amplified tone signal from amplifier 40passes over path 42 to excite the lamp 22 (and thereby to impose tonefrequency modulation on the photocell output), and also passes to theganged potentiometers 44 and 46. The common control shaft of thesepotentiometers is designated in Fig. l by numeral 100, and carries aclutch plate or element 102. A control knob 104 is carried by aconcentric shaft 106 also terminating in a clutch plate 108, heldnormally spaced from clutch element 102 by a spring 110 urging knob 104outwardly from the engaged position. A switch 112 is arranged so thatwhen knob 104 is depressed to engage the clutch elements for making ablack level adjustment, the channel 114 from tone amplifier 40 isinterrupted, and the output lead or channel 116 from the switch isgrounded to render ineffective certain parts now to be described. Thearrangement of this switch for operation upon depressing knob 104 ismerely illustrative, since other arrangements, including a separatemanual switch, could be employed for the same purpose.

When the switch 112 is in the position shown in Fig. 1, a circuit iscompleted from lead or channel 114 to the lead 116 passing to anotherset of two ganged potentiometers numbered 118 and 120, the commoncontrol of which is shown as a manually operable knob 122 labeledprinting control. In its other position, the switch short circuits thepotentiometers 118, 120.

Bearing in mind that the purpose of the invention is 7 to modify theaction of the engraving in accordance with the operators knowledge ofthe intended use of the finished engraving, as regards the printingprocess, paper, ink and the like to be employed, it will be realizedthat the modification in machine characteristic is not concerned withthe character of the original copy, which may be assumed to be of normaltonal scale. Hence, the setting of the black level control 104 must bemade without the introduction of any effect from the printing control122 and its associated circuits. This is the reason for the provision ofswitch 112.

In making the printing control adjustment, it is essential that it beaccomplished before at least the white level copy is in position tocontrol the cell output.

- age source 124.

setting has been made. However, since ordinarily more than one plate isto be made from an original for one printing run, the adjustment willnot have to be repeated for every plate. Thus, it is recommended that inpractice, the printing control adjustment be accomplished (if it is tobe used' at all) before both the black and white level settings aremade;

With the copy to be scanned in place on cylinder 10 and a' plate securedto cylinder 12, and with the machine running but the clutchesdisengaged, and with the stylus out of engagement with its surface, theprocedure may be as follows. The printing control knob 122 ismanipulated to a setting corresponding to the type of printing processto be used (ink, paper and so forth). Carriage 20 and cylinder 10 areset so that a blackest part of the Knob 104 is depressed and rotated toproduce a predetermined minimum hole size in a test portion (edge) ofthe engraving blank, as described in the prior patent and applicationreferred to above. Depression of knob 104 cancelled the efiect ofpotentiometers 118, 120, although a separate switch could have been usedfor this purpose. Thereafter, thecylinder l0 and carriage 20 areadjusted to scan a whitesfportion of the copy, and the white levelsetting made by the potentiometer controlled volt- The'carriagesarereturned to their starting positions, the clutches engaged to drivecylinder 10 (and the carriages by tape 30), and the stylus engaged withthe sheet to be engraved.

The proper setting of control 122 may be established i by reference toexperience, but more systematically, the

gee-sees areas of the plate) which the machine'will-produce. The

knob 122 will accordingly. preferably be providedwith a scale andpointer, 'or'other'means permitting its accurate positioning.

The normal adjustment procedure for black and white levels willordinarily produce a certain, unchanging minimum hole size intheengraving, because the adjustment of black level ismade'while'visually observing the pits produced as the knob 104 isadjusted, as fully described in the prior patent. With the machine inthis condition, the printing control'co'rrection cannot be made bysimply increasing the signal amplitude from potentiometer 44, because todo so would alter the over-all characteristic of the machine. Forexample, an increase in this amplitude to provide a larger minimum holesize for a certain printing process will increase the stylus travel forall parts of the plate or original, and since the photocell output levelwould be unchanged, the whitest portions of the plate might becompletely devoid of plate surface. A certain minimum size of islandsbetween pits must be maintained even in the white areas of the plate ifsatisfactory printing is to be done.

The above circuit provides for altering the minimum hole size that willbe produced in the darkest areas of the plate, by potentiometer 118, andautomatically makes a corrective change in the effective photocelloutput amplitude, by reason of the potentiometer 120, so that therequirement of a certain shape of machine characteristic (and a certainmaximum penetration even in the white plate areas) is maintained.

During the making of the essential black signal level adjustment, andwith knob 104 depressed to ground circuit 116, there will of course bezero output from the ganged potentiometers 118 and 120. Therefore, thefractional tone output from potentiometer 44 passes unmodified throughadding circuit 124 and is subtracted as by circuit 126 from thephotocell output amplified at 128. The resulting signal passes throughtone compensator 130 and adding circuit 132 to the power amplifier andstylus motor 28. Adding circuit 132 accomplishes the addition of anotherfraction of the amplified tone generator output from potentiometer 46passing through adding circuit 134, but the latter does not modify suchfraction in any way because there is zero output from potentiometer 120at this time.

When the initial adjustments for printing parameters and the black andwhite signal levels have been completed, and the engraving commenced, amodified signal will be delivered to the power amplifier by adding theportion derived from 118, via adding circuit 124, to the signalsubtracted from the photocell output in subtracting circuit 126. Also,the related fraction of the amplified generator output frompotentiometer 120 is added at circuit 134 to the fraction derived frompotentiometer 46 so that a composite added signal is furnished to addingcircuit 132 to modify the final signal delivered to the power amplifier.

The description above pertains to a machine employing tone compensation(element 130) for making possible good results in fine screen work. Forcoarser screens or lower quality of engravings, the compensator circuitmay be omitted, in which case the potentiometers 44 and 118 will beunnecessary and will be omitted. The nature of the tone compensationsystem is fully described in the copending application of J. A.Boyajean, Serial No. 248,755, filed September 28, 1951, now Patent No.2,777,058, January 8, 1957, to which reference may be made for details.

Fig. 2 of the drawings shows graphically the change in reproductiondensity (obtained from an engraving when used in the selected printingprocess) introduced by the printing control circuits of the invention.The minimum hole size produced has been reduced by the amount indicated,at higher values of photographic density of the original, without muchchange in the over-all characteristicof the machine-for lower values ofphotographic density.

The adding and subtracting circuits of Fig. 1 may utilize either voltageaddition and subtraction, or current addition and subtraction. Suitablecircuits for these purposes are well known in the electronic field, butspecific examples thereof are shown in Figs. 3 and 4. Fig. 3 representsa typical voltage adding circuit which combines the functions of theadders 132 and 134 of Fig. 1. In Fig. 3, numerals 136, 138 and 140indicate three trans formers whose primary windings are supplied withsignals (to ground) representing the signals from potentiometer 46,potentiometer and compensator of Fig. 1. The secondary windings of thetransformers (or selected fractions thereof, as indicated by the taps142) are connected in series to deliver to the control electrode orinput circuit of the following power amplifier a composite signalproportional to the sum of the three inputs. Where the transformers aremade especially for a particular application, they can readily bedesigned so that the single output is obtained from a single secondarywinding on a common core which also carries the three primary windings.

In Fig. 4, a similar circuit is illustrated, but which combines thefunctions of the adder 124 and subtractor 126 of Fig. 1. In this case,in which similar reference numerals are used to indicate the sameelements as in Fig. 3, one of the secondary windings, designated 144, isreversed in phase (by reversal of terminals) to accomplish thesubtraction of the signal from amplifier 128 from the sum of the signalsfrom potentiometers 118 and 44.

While the invention has been described, by way of example, in connectionwith a preferred embodiment, it is to be understood that many variationsthereof. and in its implementation, will occur to those skilled in thisart. Therefore, the description above is to be taken as merelyillustrative, and the invention is intended to include all suchmodifications as fall within the scope of the appended claims.

What is claimed is:

1. In a photo-electric engraving apparatus of the type having aphotocell for sensing the reflection density of an original, and a lightsource for exciting said photocell, an engraving stylus and motortherefor for engraving a plate in accordance with signals derived fromsaid photocell, a screen generator connected to said light sourcethereby to modulate the output signal of said photocell, and means forapplying a part of the output of said generator to said stylus motor,the improvement which comprises an adjustable printing control includinga first circuit means for deriving from said generator a first signalportion and for adding the same to the signal applied to said stylusmotor, a second circuit means for deriving a second signal portion fromsaid generator and for subtracting the same from the signal derived fromsaid photocell means, and means for combining the resulting modifiedsignals and applying the same additively to said stylus motor.

2. Photoelectric engraving apparatus in accordance with claim 1,including manually operable control means for concomitantly adjustingthe magnitudes of the signals derived by said first and second circuitmeans.

3. Photoelectric engraving apparatus in accordance with claim 1,including manually operable switch means for simultaneously disablingsaid first and said second circuit means.

4. Apparatus in accordance with claim 2, in which said adjusting meanscomprises a pair of potentiometers con nected respectively in thecircuits of said first and second circuit means, and ganged manualcontrol means for operating said potentiometers.

5. A control arrangement for photoelectric engraving machines of thetype having photoelectric pickup meansengraving means, and a constantfrequency tone generator connected to both.said photoelectric pickupmeans and said engraving means to energize the latter'with a compositesignal derived from said .tone generator and from the output of saidphotoelectric means as modulated by said tone generator, comprising afirst circuit means for deriving an adjustable portion of said generatorsignal 8 a minimum selected amplitude of engraving, said printingcontrol means comprising third circuit means for deriving a furtheradjustable portion of the output of said tone generator and subtractingthe same from the output of said photocell, fourth circuit means forderiving a still another adjustable portion of the output of saidgenerator and adding it to the composite signal applied tosaid'engraving means, and means for concomitantly adjusting the portionsof said generator signal derived by 10 said third and fourth circuitsmeans.

No references cited.

